1. Field of the Invention
The present invention relates to balloon catheters for treating the luminal systems of a patient. Specifically, the invention relates to catheters having a flexible membrane positioned at a distal portion of the catheter where the flexible membrane is retained in a substantially unexposed conformation prior to deployment. Preferably the flexible membrane is capable of delivering a therapeutic agent to a localized environment when deployed to an exposed conformation.
2. Description of the Related Art
Heart and vascular disease are major problems in the United States and throughout the world. Conditions such as atherosclerosis result in blood vessels becoming blocked or narrowed. If this blockage or narrowing of a vessel occurs in the coronary arteries supporting the heart, which deliver oxygenated blood, this will have significant consequences, since the heart muscle must be well oxygenated in order to maintain its blood pumping action.
Occluded, stenotic, or narrowed blood vessels may be treated with a number of relatively non-invasive medical procedures including percutaneous transluminal angioplasty (PTA), percutaneous transluminal coronary angioplasty (PTCA), and atherectomy. Such angioplasty techniques typically involve the use of a balloon catheter. Commonly, the balloon catheter is initially advanced over a guidewire so that the balloon is positioned adjacent a stenotic lesion. Once in place, the balloon is then inflated, and the restriction of the vessel is opened.
Typically, balloon catheters are structured such that they have a balloon fastened at least at one end around the exterior of a hollow catheter shaft. The hollow interior of the balloon is in a fluid flow relation with the hollow interior of the shaft. Fluid under pressure can thereby be supplied to the interior of the balloon through the shaft in order to expand the balloon against an obstruction.
Presently catheter balloon materials may be classified as compliant, semi-compliant, or non-compliant balloons. Compliance can be defined as the increase in the balloon diameter above nominal balloon pressure. Generally, non-compliant balloons have less increase in diameter, than semi-compliant balloons, which in turn have less increase in diameter than compliant balloons.
Compliant balloons expand and stretch with increasing pressure within the balloon, and are made from such materials as silicone, thermoplastic elastomers (TPEs), and polyethylene or polyolefin copolymers. Non-compliant balloons, made from such materials as polyethylene terephthalate (PET) or polyamides, remain substantially at a pre-selected diameter as the internal balloon pressure increases beyond that required to fully inflate the balloon.
Compliant balloon materials provide a degree of softness to the balloon which aids its passage through, and expansion within, e.g., blood vessels. Known compliant balloon materials also can display good abrasion and puncture resistance at thicknesses typically used for medical device balloons. In light of the foregoing, it is one object of the present invention to provide a balloon catheter that employs a compliant balloon.
It is an object of the present invention to provide a device that is useful for recovering a balloon predictably and compactly upon deflation to facilitate in vivo movement of the balloon catheter.
In addition to the above-described uses of balloon catheters in PTA, PTCA, and atherectomy, some balloon catheters are made to deliver therapeutic drugs or agents. For example, some balloon catheters deliver a systemic bolus of liquid that includes a drug to a targeted tissue location using an open catheter lumen or channel located at some length along the catheter shaft. Alternatively, the drug can be delivered by coating it on the exterior of the balloon. Unfortunately, when such delivery methods are used to deliver a controlled volume of medication to a desired tissue location, medication may be lost to systemic circulation either because of an inability of the drug to quickly penetrate local tissue, or because the drug coating has been washed away.
In general, liquid formulations containing a drug or agent that are delivered to a targeted tissue location by liquid bolus may not penetrate the tissue sufficiently at the targeted tissue location to result in a significant therapeutic effect, and may be washed away by body fluids. Similarly, drug coated on the surface of a balloon can be washed away due to contact with a circulatory environment, as the circulatory environment matches the environment the drug is designed to target. Such systemic dilution substantially diminishes the effectiveness of the drugs or agents, and increases the likelihood of a greater systemic effect caused by the quantity of drug or agent washed into the bloodstream.
In light of the foregoing, there is a need for an improved balloon catheter capable of delivering therapeutics in a safe and effective manner to targeted tissues within the body. The present invention includes embodiments directed toward solutions that address this unmet need.